From WO 2011/121500 A2 a method for locating persons and/or mobile machines in mine workings by utilizing the RFID technology is known. In order to be able to reliably locate persons or machines with minimized use of energy of the plant, neighbouring transmitting units are driven in such a manner that they radiate their transmitter signals in succession so that information about the current location of the machine or person provided with a tag can be obtained from the position of a receiving unit which first receives a transponder signal of an activated personal or machine tag. By changing the signal field strength of the transmitter signal, it is then possible to draw a conclusion with respect to the distance of the tag from the nearest receiving unit. For a face surveillance system with shield supports, conveyor and extraction machine moving along the conveyor, a reference tag can be provided additionally at the conveyor in order to ensure via the reception of the transponder signal of the reference tag that the transmitter signal radiated completely covers the space located between the reference transponder and transmitting unit and to be surveyed because it is only this space which forms a possible habitable space for persons or personal tags worn by them.
An object of the present disclosure might be to increase the operational safety of the RFID technology. A further optimization of the energy consumption might also be of interest.